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.c om ng cu u du o ng th an co Technical Review – Materials :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com https://fb.com/tailieudientucntt Stress: N/m2, Pa or psi σ = P/A0 P: load on the sample A0: original(zero-stress) cross sectional area Strain: unitless ε = (l-l0)/l0 = Δl /l0 l : sample length l0: original(zero-stress) length cu u du o ng th an co ng c om Basics – Mechanics of Materials :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com https://fb.com/tailieudientucntt σ c om Hooke’s law σ = Eε E: Young’s modulus or elastic coefficient E an co ng th ε ng Yield strength The stress at which a material exceeds its elastic limits and the material begins to deform permanently cu u du o :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om ng co cu u du o ng th an Maximum tensile stress that a material withstand without rupture ε :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com https://fb.com/tailieudientucntt Shear stress and strain c om τ= F/A th an co ng Shear modulus: G G = shear stress/shear displacement angle = τ/γ = (F/A)/(ΔX/L) ΔX Area, A cu u du o ng F L :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com https://fb.com/tailieudientucntt F Poisson’s ratio Under axial load, ε(axial) = Δl /l0 ε(transverse) = Δd/d0 Poisson’s ratio; ν = transverse strain/longitudinal strain = -ε(transverse) / ε(axial) Typical values are 0.2 to 0.5 Relation of E and G E=2G(1+ ν) cu u du o ng th an co ng c om :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om SCS(Single Crystal Silicon) ng co an th ng du o u Anisotropic : crystal Elastic : catastrophic failure Young’s modulus = 190GPa < 200(SS) Hardness = 850 kg/mm2 > 660(SS) Yield strength = 7x 109 N/m2 > 2.1x109(SS) Mightier than we think ! cu :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om ng co an th ng du o u cu From Kovacs :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com https://fb.com/tailieudientucntt Limiting factors - Crystallographic defects and planes - Residual stress from high temperature process and film structure th How to overcome? - Stress consideration from design stage - Minimize defects during dicing, grinding and polishing - Tribological measure: coating and lubrication - Low temperature process cu u du o ng an co ng c om :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com https://fb.com/tailieudientucntt Because of anisotropy of cubic system, elastic coefficient is 6x6 matrix in the form of, C11 C12 C12 0 Cij = 0 C12 C11 C12 0 C12 C12 C11 0 0 C44 0 0 0 C44 0 0 0 C44 cu u du o ng th an co ng c om for [100] axis loading :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com 10 https://fb.com/tailieudientucntt ng c om Dry and wet oxidation Si + O2 → SiO2 Si + 2H2O → SiO2 + 2H2 du o O-O cu u O-O ng th an co Molecular density of Si = x 1022 atoms/cm3 Molecular density of SiO2 = 2.2 x1022 molecules/cm3 Oxide film expands → compressive stress t SiO2 0.44t :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com 47 https://fb.com/tailieudientucntt .c om ng co an th ng du o u cu :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com 48 https://fb.com/tailieudientucntt ng co an th ng du o u Strong mechanical property, E=448 GPa (190GPa for Si) Chemical stability at high T Strong resistance to oxidation even at high T Passivation layer Wide bandgap even at 300K (2.996 at 300K, 3.03 at 0K for a-SiC) Single crystal, polycrystalline and amorphous can be formed by MOCVD, MBE, PECVD, etc SiH4 + CH4 → SiC(s) + 4H2 Doping, etching and metallization: possible but limited Good candidate for harsh environment MEMS cu c om Silicon carbide :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com 49 https://fb.com/tailieudientucntt Material Properties of SiC 1-D polymorphism: polytypism Identical planar arrangement but with different stacking sequence Crystal structure: Cubic, Hexagonal, Rhombohedral 3C-SiC, 6H-SiC, 4H SiC cu u du o ng th an co ng c om Crystal system Number of layers in a period along stacking direction :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com 50 https://fb.com/tailieudientucntt Stacking of planes cu u du o ng th an co ng c om :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com 51 https://fb.com/tailieudientucntt 3C-SiC Structure cu u du o ng th an co ng c om :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com 52 https://fb.com/tailieudientucntt 6H-SiC 4H-SiC cu u du o ng th an co ng c om :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com 53 https://fb.com/tailieudientucntt .c om ng co an th ng du o u cu :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com 54 https://fb.com/tailieudientucntt Crystal growth 2-4” 6H-SiC can be grown with sublimation onto SiC seed at 2000oC Epitaxial growth 6H-SiC: APCVD with Silane and Propane source at 15001700oC over 6H-SiC 3C SiC: APCVD with Silane and Propane source at 15001700oC over Si Ỉ heteroepitaxy Mismatch in lattice constant 0.436nm(SiC) and 0.543nm(Si) can be overcome with carbonization Ỉ convert near surface Si to 3C-SiC by heating and reaction with C Ỉ Grow 3C-SiC over carbonization layer cu u du o ng th an co ng c om :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com 55 https://fb.com/tailieudientucntt .c om ng co an th ng du o cu u Rajan, N., et al., "Fabrication and Testing of Micromachined Silicon carbide and Nickel Fuel Atomizers for Gas Turbine Engines", Journal Of Electromechanical Systems, vol.8, no 3, Sept 1999 Yasseen, A.A., et al., "Surface Micromachining of Polycrystalline SiC Films Using Microfabricated Molds of SiO2 and Polysilicon", Journal of Microelectromechanical Systems, vol 8, no 3, Sept 1999 :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com 56 https://fb.com/tailieudientucntt cu u du o ng th an co ng c om Metal films :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com 57 https://fb.com/tailieudientucntt an co Used increasingly for microfluidic and biochemical applications Light weight, easy processing, low cost, high electrical resistance, corrosion resistance, flexibility in engineering properties ng c om Organic materials th ng du o u Photoresist Polyimide Parylene Conductive polymers PVDF (polyvinyldifluoride) PMMA(polymethylmethacrylate), PC(polycarbonate), PTFE(polytetrafluoroethylene), PDMS(polydimethylsilane) cu :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com 58 https://fb.com/tailieudientucntt Teflon® - PTFE (Polytetrafluroethylene) high chemical inertness good thermal stability up to ~200°C Extremely low friction coefficient Thermoplastic Lexan® - PC (Polycarbonate) High stiffness and strength Thermal stability up to ~135 °C High surface toughness and rigidity Relatively low stability to chemical attack PEEK (Polyetheretherketone) Excellent chemical resistance Very high operating temperature ~ 250 °C Good dimensional stability Low moisture absorption even at elevated temperatures High cost cu u du o ng th an co ng c om :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com 59 https://fb.com/tailieudientucntt Kynar® - PVDF (polyvinyldifluoride) Good chemical resistance Thermal stablity upto ~ 140°C High surface rigidity and strength Virtually no absorption of water Ultem® - PEI (Polyetherimide) Amorphous material Material properties show small change over wide range of temperature Excellent chemical resistance Thermoplastic Widely utilized for medical application PDMS (Polydimethylsiloxane); Silicone, RTV - Biocompatible and flexible - Low toxicity, No solvents or cure byproduct - Cures to a transparent, flexible elastomer - Low water adsorption - Stability over wide temperature range ( from-55 to 200C) cu u du o ng th an co ng c om :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com 60 https://fb.com/tailieudientucntt References cu u du o ng th an co ng c om S M Sze, “Semiconductor Sensors”, Wiley, 1994 C S Smith, “Piezoresistance Effect in Germanium and Silicon”, Phys Rev., 42-48, 94(1), 1954 Y Kanda, “Piezoresistance effect of silicon”, Sensors and Actuators A, 83-91, 28, 1991 L Ristic, “Sensor Technology and Devices”, Artec House, 1994 Kovacs, “Micromachined Transducers Sourcebook”, McGraw-Hill, 1998 Hsu, “MEMS and Microsystems”, McGraw-Hill, 2001 Mehregany et al, "Silicon Carbide MEMS for Harsh Environments", Proceedings of IEEE, 1594-1609, vol 86, no.8, 1998 Zorman et al.,"Silicon carbide for MEMS and NEMS - An Overview", Proceedings of IEEE Sensors, 1109-1114, vol 2, 2002 :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com 61 https://fb.com/tailieudientucntt ... Dry and wet oxidation Si + O2 → SiO2 Si + 2H2O → SiO2 + 2H2 du o O-O cu u O-O ng th an co Molecular density of Si = x 1 022 atoms/cm3 Molecular density of SiO2 = 2. 2 x1 022 molecules/cm3 Oxide film... anisotropy of cubic system, elastic coefficient is 6x6 matrix in the form of, C11 C 12 C 12 0 Cij = 0 C 12 C11 C 12 0 C 12 C 12 C11 0 0 C44 0 0 0 C44 0 0 0 C44 cu u du o ng th an co ng c om for [100] axis... n-Si ρ (Ohm-cm) π11 7.8 6.6 11.7 -1 02. 2 π 12 -1.1 53.4 π44 138.1 -13.6 :: EAM 5715 Electronic Devices for Human Interface Systems (EDHIS) CuuDuongThanCong.com 23 https://fb.com/tailieudientucntt
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